1. Rub the leg of lamb with the lemonjuice, 1 tbsp salt and the thyme leaves.
2. Allow to tenderise for an hour.
3. In a food processor, mix the yoghurt with the rest of the ingredients (except the rosemary) to create a marinade.
4. Leave for 2-3 hours, or preferably overnight.
5. Heat the oven 230C/gas 8.
6. Place the meat in a roasting tray over a bed of rosemary and cook for around 40 minutes (or less if you prefer rare).
7. Leave to rest for 15 minutes, then serve with flat bread and a green salad.